TELOMERASE ACTIVITY AND DYNAMICS OF TELOMERIC DNA IN FISH

In fish like in other vertebrates telomeric DNA is consisted of thousands of repeats of non-coding TTAGGG sequences. The length of the telomeric DNA in fishes varies from2000 to 20000 of base pairs. In contrast to mammals, where telomerase activity is limited, telomerase in fish is presentin all tissues and cells through the entire life. Research performed on the model organisms including zebrafish (Danio rerio) and medaka (Oryzias latipes) showed that the activity of telomerase is the highest in young, fast growing individuals and in the regenerating tissues. Length of telomeric DNA in fish extends and decreases depending on the activity of telomerase and development stage of the fish. However, in spite of telomerase activity, in matured fish telomeres start to shorten gradually. Genetic sex and environmental conditions seem to affect rate of the telomere shortening. In poikilothermic organisms, environmental stress, such as extremely low or high temperatures can induce oxidative stress that accelerates process of telomere shortening. Knock out of the TERT gene encoding one of the telomerase components does not affect condition of the young individuals. Negative consequences of the limited telomerase activity in fish tissues occur only in the adult specimens and lead to reduced fertility, atrophy of the internal organs, skeletal muscle loss and increased mortality. These symptoms are similar to the premature senescence. Reviewed here results of the research focused on telomerase activity and dynamics of the telomeric DNA demonstrate that at least some of the fish species are excellent models in studies concerning senescence, tissue regeneration and impact of the environmental stress on the telomere shortening.